Add tls config options

[boggyhole]

Allow mutual tls client configuration, adding root CAs and tls
verification

FIxes: #103

[codecov-commenter]

Codecov Report

Merging #104 (2196a39) into master (41ab260) will decrease coverage by 1.10%.
The diff coverage is 70.74%.

@@            Coverage Diff             @@
##           master     #104      +/-   ##
==========================================
- Coverage   71.99%   70.90%   -1.09%     
==========================================
  Files           9        9              
  Lines         589      615      +26     
==========================================
+ Hits          424      436      +12     
- Misses        132      144      +12     
- Partials       33       35       +2     

Impacted Files	Coverage Δ
main.go	71.60% <68.58%> (-3.40%)	⬇️
attacker/attacker.go	67.80% <83.34%> (+1.76%)	⬆️
gui/drawer.go	70.87% <0.00%> (-1.57%)	⬇️

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[nakabonne]

Looks neat. Thanks a lot!